Ionisation chamber



Nov. 1-7, 1959 R. e; DAVIS IONISATION CHAMBER Filed Nov. 9, 1955 I v Inventor;

Ron/2r a. DAVIS -'1M,eM-,'/A n i Attorneyn IONISATION CHAMBER Robert G. Davis, Southend-on-Sea, England, assignor to E. K. Cole Limited, Southend-on-Sea, England Application November 9, 1955, Serial No. 545,960

Claims priority, application Great Britain November 11, 1954 9 Claims. (Cl. 313-93) This invention relates to apparatus in which an ionisation is eflected by rays from a radioactive source in a chamber containing an electrode for collecting ions. A specific application (there are other applications) is to a beta measuring gauge such as is used for example for measuring or indicating the mass between a source of beta rays and an ionisation chamber.

it is usually necessary in such apparatus that during use the air or other ionisable medium (usually a gas) should be saturated, i.e. that the potential between the electrodes (usually the walls of the chamber and a collecting electrode) be such that the negative and positive ions are not able to' re combine as neutral atoms. It is required that as large a volume as possible of the ionisable medium within the ionisation chamber shall be subject to ionisation, which means that as small a space as possible should be occupied by the collector electrode. However, for eflioient saturation the collector electrode should be as close as possible to the other electrode. Thus these requirements are in conflict.

An object of the present invention is to provide an ionisation chamber in which this conflict is substantially resolved.

One feature of the present invention is an ionisation chamber for use in conjunction with a radioactive source and containing a collector electrode which is permeable by beta radiation. Y

Another feature of the invention is an ionisation chamber for use in conjunction with a radioactive source, in which an extension from a metal wall of the chamber extends within the collector electrode.

A further feature of the invention is an ionisation chamber for use in conjunction with a radioactive source, comprising a collector electrode within the chamber, a metal wall to said chamber, and a metal body extending within said collector electrode and electrically connected with said wall.

The collector electrode is conveniently rendered permeable by beta rays by making it foraminous, for example it may be of perforated or mesh form. A foraminous electrode will also usually be permeable by alpha rays or low-energy gamma rays.

The above and other features of the invention will be more readily understood by a perusal of the following description, having reference to the accompanying drawings, in which Figure his a sectional side elevation of an ionisation chamber according to the invention, Figure 2 is a perspective view of part of the chamber, and Figure 3 is a perspective view of a modified form of that part of the chamber which is shown in Figure 2.

The ionisation chamber illustrated has a wall 1 forming part of a sheet metal casing mounted on an insulating base 2 (e.g. of thermosetting resin) which also supports a cylindrical collector electrode 3. The whole assembly is outwardly of a rectangular box-like shape. 4 is a metal shield constituting the usual guard ring or plate, which is earthed when the chamber is in use, the collec- 1 tor'electrodei3 beingfinsulated from the shield 4' by' means of ceramic bushes as shown in Figure 1. The chamber r" V P t tedv NOV'-- has a window 5 (e.g. of aluminium foil) clamped against an opening in the casing. At 6 and 7 respectively are shown, in diagrammatic outline only, a source of beta rays for use in conjunction with the ionisation chamber, and a guide through which material under test may be passed between the source 6 and the window 5 of the ionisation chamber.

Radiation from the source 6 passes through the window 5 into the chamber and ionises the atmosphere therein. The chamber casing and the collector electrode 3 are given appropriate potentials to cause a saturation ion current to flow. As shown the collector electrode 3 is of perforated form, being stamped out of sheet metal and shaped, as shown in Figure 2, to a cylinder of square cross-section. This perforation of the collector electrode renders it permeable by beta radiation, permitting ions to be formed both inside and outside the collector electrode,

foil [10 is mounted on a suitable support 11.

To enable the ions formed within the collector electrode to be collected, II virtually extend the metal wall 1 of the chamber casing into the collector electrode by means of a metal rod or tube 8, secured and electrically connected to the chamber walls at 9 and disposed substantially symmetrically with respect to the longitudinal axis of the collector electrode. if desired, this tube or rod may be perforated as shown in Figure l. It is not essential that the tube or rod -8 be disposed symmetrically as shown, but such a disposition will generally be found to give optimum results.

- [n the case where high-energy gamma radiation is employed (for example, where the radioactive source is Go), there is no necessity for the collector electrode to be foraminous or of thin metallic foil since the radiation will readily penetrate the wa1l(s) of the collector electrode.

1 claim:

1. In apparatus for use in conjunction with radioactive radiation, an ionisation chamber, a collector electrode permeable to beta radiation and located within said chamber, a metal wall to said chamber, and a metal body extending within said collector electrode and electrically connected with the said wall.

2. In apparatus for use in conjunction with radioactive radiation, an ionisation chamber, a collector electrode permeable to beta radiation and located within said chamber, a metal wall to said chamber, and an extension from said wall electrically connected therewith and extending within said collector electrode.

3. An ionisation chamber according to claim 1, the collector electrode being formed of perforated sheet metal.

4. An ionisation chamber according to claim 1, the col lector electrode being formed of thin metallic foil.

5. An ionisation chamber according to claim 2, the collector electrode being formed of perforated sheet metal.

6. An ionisation chamber according to claim 2, the collector electrode being formed of thin metallic foil.

7. An ionisation chamber according to claim 2, the said extension being disposed symmetrically with respect to the longitudinal axis of the said collector electrode.

a 4 8. v.An ionisation chamber according to claim 2, the References Cited in the file of this patent said extension comprising a metal tube secured to the said UNITED STATES PATENTS wall.

9. An ionisation chamber according to claim 2, the 97,213 Dowmng Feb. 14, 1950 said extension'co'mprising a metal rod secured to the said 5 9, Goldsteln e a1 1950 wall. 2,683,234 Lynch July 6, 1954 

